Lighting Design Glossary

Altitude
Solar Altitude

(Terms of mathematics/geometry and daylighting)

The angle between a vector and the its projected
vector onto a plane it intersects. More general, the
angle between the vector and the "horizon" of the plane.
This is the counterpart of the polar angle.

Solar altitude is the angular distance
of the sun to the horizon from the view of an observer.
Of course, every other heavenly body also has its
altitude.